Hydromechanical transmission and control method

ABSTRACT

Methods and systems for a hydromechanical transmission are provided herein. In one example, the transmission system includes a hydraulic pump and a hydraulic motor rotationally coupled in parallel with a first planetary gear set and a second planetary gear set. In the system, sun gears of the planetary gear sets are rotationally coupled to the hydraulic motor, a carrier of the first planetary gear set is rotationally coupled to a first clutch and a second clutch, and a ring gear of the second planetary gear set is rotationally coupled to a third clutch.

TECHNICAL FIELD

The present disclosure relates to a hydromechanical transmission and amethod for adjusting transmission drive range.

BACKGROUND AND SUMMARY

Hydromechanical transmissions enable performance characteristics (e.g.,efficiency, shift quality, drive characteristics, control response, andthe like) from mechanical and hydrostatic transmissions to be blended tomeet certain design objectives. Some hydromechanical transmissions,referred to in the art as hydromechanical variable transmissions (HVTs),provide continuously variable gear ratios. Hydromechanical transmissionsmay be particularly desirable due to their efficiency and power take off(PTO) capabilities. Vehicles used in industries such as agriculture,construction, mining, material handling, oil and gas, and the like havetherefore made use of HVTs.

U.S. Pat. No. 7,530,914 B2 to Fabry et al. teaches a hydromechanicaltransmission with two synchronizers and two clutches. The synchronizingdevices and clutches work in conjunction to shift the transmissionbetween high and low speed ranges in both forward and reverse operatingmodes. In U.S. Pat. No. 7,530,914 B2, each clutch is paired with asynchronizing device on a common shaft. Further, each of the pairs ofclutches and synchronizers are spaced away from one another due to thepackaging constraints imposed by the transmission assembly.

The inventors have recognized several drawbacks with Fabry'stransmission as well as other hydromechanical transmissions. Fabry'ssynchronizers, for example, may be susceptible to degradation, whichgenerally decreases transmission reliability. Furthermore, thesynchronizing devices increase system cost and complexity. Otherhydromechanical transmissions have made unwanted tradeoffs with regardto transmission complexity, packaging efficiency, operational driveranges, and shifting smoothness.

To address at least a portion of the abovementioned issues, theinventors have developed a transmission system. The transmission systemincludes a hydraulic pump and motor. The hydraulic motor is rotationallycoupled in parallel with a first and a second planetary gear set. In thesystem, sun gears of the first and second planetary gear sets arerotationally coupled to the hydraulic motor. Further, in the system, acarrier of the first planetary gear set may be rotationally coupled to afirst clutch and a second clutch. Additionally, a ring gear of thesecond planetary gear set may be rotationally coupled to a third clutch.Providing a transmission with sun gears and clutches with this layout,allows the system to realize a compact design and a targeted number ofavailable drive ranges.

Further, in one example, the first clutch may be a first forward driveclutch and the second clutch may be a reverse drive clutch arrangedadjacent and coaxial with the first forward drive clutch. Positioningthe clutches in this manner increases transmission space efficiencywhile allowing the system to achieve a first forward drive range and areverse drive range.

In another example, the transmission system may include a mechanical PTOan input shaft that receives rotational input from a motive powersource. Providing the mechanical PTO further increases the system'sadaptability and allows the system to be used in a wider variety ofvehicle applications, if so desired.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a vehicle with a hydromechanicaltransmission.

FIG. 2 is first example of a hydromechanical transmission system.

FIGS. 3-8 are illustrations of the hydromechanical transmission system,depicted in FIG. 2, operating under different conditions in the system'sdrive ranges.

FIG. 9 is a chart indicating the configurations of the clutches in thedifferent drive ranges.

FIG. 10 is an exemplary diagram of the hydrostatic ratio vs. thetransmission ratio in the different drive ranges.

FIGS. 11-12 are exemplary diagrams of pump swivel angle vs. hydrostaticratio in the hydrostatic assembly.

FIG. 13 is a method for operating a transmission system to shift betweendrive ranges.

FIG. 14 is an exemplary diagram of a transmission power limit curve.

FIG. 15 shows exemplary diagrams of transmission speed ratio vs. timeand transmission pulling torque vs. time.

FIG. 16 shows exemplary diagrams of clutch differential speeds vs. timeand clutch pressures vs. time.

FIG. 17 shows exemplary diagrams of hydrostatic motor torque vs. timeand clutch pressures vs. time.

FIG. 18 shows an example of a reverse shift operation in thetransmission depicted in FIG. 1.

DETAILED DESCRIPTION

A hydromechanical transmission and method for operation of thetransmission is provided herein. The hydromechanical transmissionenables synchronous shifting to occur in a space efficient package. Thetransmission includes one reverse clutch and two forward clutchescoupled in parallel to one another as well as a first and a secondplanetary gear set to achieve a desired set of operating drive ranges.In one example, the reverse clutch and one of the forward drive clutchesmay be rotationally coupled to a common shaft. This twin clutch designmay enable manufacturing costs to be decreased and enable thetransmission to achieve a more compact design. Further, in such anexample, the second forward drive clutch may rotate on a shaft offsetfrom the other clutches and planetary assemblies. In this way, thetransmission may achieve a targeted degree of drop (e.g., a distancebetween the input and output interfaces). Further in one example, ahydrostatic assembly in the transmission may be a U-shaped hydrostaticunit where the mechanical input shafts for a hydraulic pump (e.g.,variable displacement pump) and a motor (e.g., fixed bent axis motor)that are parallel to one another and arranged on one side of the unit.This permits the unit's size to be reduced and avoid the use of highpressure hoses to reduce manufacturing costs as well the chance ofhydrostatic unit degradation.

In the transmission, a hydrostatic branch, which includes a hydraulicmotor and a pump, are arranged in parallel with mechanical branches andcoupled to a motive power source (e.g., an engine, an electric motor,combinations thereof, or other suitable prime mover). In one example,sun gears of the planetary gear sets are rotationally coupled to oneanother and the hydrostatic branch. Because the sun gears are attachedtogether the transmission may achieve greater space efficiency.

The shifting strategy employed in the system may include, holding one ofthe clutches open, while synchronously opening and closing the remainingclutches. Such a shifting strategy may be used to smoothly transitionbetween two drive ranges in a group of drive ranges that includes areverse drive range and two forward drive ranges. Consequently, powerinterruption and noise, vibration, and harshness (NVH) during shiftingtransients may be reduced (e.g., avoided). Further, the transmission'sefficiency may be increased when using this shifting strategy.

FIG. 1 illustrates a schematic depiction of a transmission system with ahydromechanical power split. FIG. 2 shows a first example of atransmission system designed to provide continuously variable input tooutput speed adjustability using a wolf symbolic scheme. FIGS. 3-8depict the first example of the transmission system in differentoperating drive ranges in which power is additively combined orrecirculated using the power split arrangement. FIG. 9 shows a chartwhich indicates the state of the clutches in the first example of thetransmission system in the different drive ranges. FIG. 10 illustratesan exemplary graph of the hydrostatic ratio vs. the mechanicaltransmission ratio in different drive ranges. FIGS. 11-12 depictexemplary graphs of pump swivel angle vs. the hydrostatic ratio in theforward and reverse drive ranges. Exemplary as used herein does notdenote any sort of preferential indication but rather signifies oneamong multiple potential configurations. FIG. 13 shows a method forsmoothly and efficiently shifting between drive ranges in a transmissionsystem. As described herein, a smooth shift is indicative of a shiftingevent in which power interruption is reduced (e.g., avoided). Thus, asmooth shift may significantly reduce or in some cases avoid powertransfer spikes or drops during shifting operation. Smooth shiftstherefore allow transmission efficiency to be increased as well asvehicle drivability and drive comfort. FIG. 14 depicts a use-case powerlimit curve for a hydromechanical transmission. FIGS. 15-17 depictdifferent diagrams with plots the embody a use-case shifting strategy.FIG. 18 shows the transmission, illustrated in FIG. 1, during reverseshifting operation.

FIG. 1 shows a schematic depiction of a transmission system 100 (e.g., ahydromechanical variable transmission) in a vehicle 102 or othersuitable machine platform. In one example, the vehicle may be anoff-highway vehicle, although the transmission may be deployed inon-highway vehicles, in other examples. An off-highway vehicle may be avehicle whose size and/or maximum speed precludes the vehicle from beingoperated on highways for extended durations. For instance, the vehicle'swidth may be greater than a highway lane and/or the vehicle top speedmay be below the highway's minimum allowable or suggested speed, forexample. Industries and their corresponding operating environments inwhich the vehicle may be deployed include forestry, mining, agriculture,and the like. In either case, the vehicle may be designed with auxiliarysystem driven via hydraulic and/or mechanical power take-offs (PTOs).

The transmission system 100 may function as an infinitely variabletransmission (IVT) where the transmission's gear ratio is controlledcontinuously from a negative maximum speed to a positive maximum speedwith an infinite number of ratio points. In this way, the transmissioncan achieve a comparatively high level of adaptability and efficiency inrelation to transmissions which operate in discrete ratios. Further, inone use-case example, the transmission may be configured to operate inan environmental temperature range from −40° C.-80° C. In such anexample, a sump, in a transmission lubrication system, may operate in arange between −40° C.-100° C. However, the transmission may be designedfor a variety of operating temperature ranges. Further, in certainexamples, the transmission system may be designed to operate on alongitudinal slope up to 35 degrees and a lateral inclination of 25degrees. Although the longitudinal slope and/or lateral inclinationthreshold may be adjusted (e.g., increased or decreased) to suitdifferent end-use design goals.

The transmission system 100 may have asymmetric maximum output speedsfor forward and reverse direction (e.g., reverse drive speed may offerapproximately 56% of the forward drive speed). This forward-reversespeed asymmetry may enable the transmission to achieve a desired breadthof speed ranges. However, other suitable output speed variations havebeen contemplated, such as symmetric output speeds in the forward andreverse directions, which may however, demand the use of an additionalclutch which may increase system complexity.

The transmission system 100 may include or receive power from a motivepower source 104. The power source 104 may include an internalcombustion engine, electric motor (e.g., electric motor-generator),combinations thereof, and the like. In one use-case example, the powersource 104 may generate greater than 80 kilowatts (kW) of power (e.g.,100-115 kW). To elaborate, the power source may be operated in the rangebetween 900-2100 revolutions per minute (RPM) with a targeted rangebetween 1200-1600 RPM, in some instances. Further, in some examples, theengine idle speed may be approximately 650 RPM. However, numeroussuitable transmission operating and idle speed ranges have beenenvisioned.

A torsional damper coupling 106 may be further provided in thetransmission. Gears 108, 110, such as bevel gears, may be used torotationally couple the power source 104 to an input shaft 112. Asdescribed herein, a gear may be a mechanical component which rotates andincludes teeth that are profiled to mesh with teeth in one or morecorresponding gears to form a mechanical connection that allowsrotational energy transfer therethrough.

A mechanical PTO 114 may be coupled to the input shaft 112. Themechanical PTO 114 may drive an auxiliary system such as a pump (e.g., ahydraulic pump, a pneumatic pump, and the like), a winch, a boom, a bedraising assembly, and the like. To accomplish the power transfer toauxiliary components, the PTO may include an interface, shaft(s),housing, and the like. However, in other examples, the PTO may beomitted from the transmission system. A gear 116 may be coupled to theinput shaft 112. A mechanical assembly 118 is further included in thetransmission system 100. The mechanical assembly 118 may include theshaft 112 and/or the gear 116 as well as shaft 167, described in greaterdetail herein. Further, the transmission may include a shaft 120 and agear 122 rotationally coupled to the gear 116 on the input shaft 112.Dashed line 124 and the other dashes lines depicted in FIG. 1 indicate amechanical connection between components which facilitates rotationalenergy transfer therebetween.

A gear 126 meshing with gear 122 may be rotationally attached to acharging pump 128. The charging pump 128 may be designed to deliverpressurized fluid to hydraulic components in the transmission such as ahydraulic motor 134 (e.g., hydrostatic motor), a hydraulic pump 136(e.g., hydrostatic pump), and the like. The fluid pressurized by thecharging pump may additionally be used for clutch actuation and/ortransmission lubrication. The charging pump may include a piston, arotor, a housing, chamber(s), and the like to allow the pump to movefluid. The mechanical assembly 118 is rotationally coupled in parallelto a hydrostatic assembly 130 (e.g., a hydrostatic unit). Further, thehydrostatic assembly 130 may have a U-shape design where the shafts 131,133 serve as a mechanical interface for the hydraulic pump 136 (e.g.,variable displacement pump) and the hydraulic motor 134 (e.g., fixedbent axis motor), respectively, are parallel to one another and arrangedon one side of the assembly. This U-shaped layout permits thehydrostatic assembly's size to be reduced and enables the use of highpressure hoses to be forgone to reduce manufacturing costs as well thechance of hydrostatic unit degradation, if desired. Still further, thehydrostatic assembly 130 may be arranged on an opposite side of thetransmission as the charging pump 128 and/or axially offset fromclutches 170, 172. Arranging the hydrostatic assembly in this mannerpermits the width and length of the transmission to be reduced andallows the installation of the transmission in the vehicle to besimplified. Further, the motor and the pump in the hydrostatic assemblymay be enclosed a common housing to increase transmission compactness.

The coupling of the hydrostatic assembly to the mechanical assemblyenables the transmission to achieve power split functionality in whichpower may synchronously flow through either path to additively combineor recirculate power through the system. This power split arrangementenables the transmission's power flow to be highly adaptable to increaseefficiency over a wide range of operating conditions. Thus, thetransmission may be a full power split transmission, in one example.

The mechanical assembly 118 may include multiple mechanical paths thatare coupled in parallel to the hydrostatic assembly. To elaborate, theshaft 167 may serve as a junction for a first mechanical path (e.g.,branch) 119 and a second mechanical path (e.g., branch) 121. The firstmechanical path 119 may provide rotational energy transfer capabilitiesfrom an interface of the hydrostatic assembly 130 to a ring gear 158 ofa first planetary gear set 148, during certain operating conditions.Additionally, the second mechanical path 121 may provide rotationalenergy transfer capabilities from the interface of the hydrostaticassembly 130 to a carrier 160 of a second planetary gear set 150.

The hydrostatic assembly 130 includes the hydraulic motor 134 and thehydraulic pump 136. Further, the hydraulic pump 136 may include a firstmechanical interface 138 and a second mechanical interface 140. Thefirst mechanical interface 138 may be rotationally coupled to amechanical bushing 132 and the second mechanical interface 140 may berotationally coupled to another mechanical PTO 142. Again, themechanical PTO may be used to drive an auxiliary vehicle system such asan air compressor, a mechanical arm or boom, an auger, and the like. Inthis way, the transmission may be adapted for a variety of end-useoperating environments. Providing multiple PTOs, in the arrangementdepicted in FIG. 1, enables the transmission system to meet end-usedesign goals in a variety of different types of vehicles, if wanted. Assuch, the system's applicability is expanded and the customer appeal ofthe transmission is increased. However, in other examples, the PTOs 114and/or 142 may be omitted from the transmission.

The hydraulic pump 136 may be a variable displacement bi-directionalpump, in one example. Further, the pump may be an axial piston pump, inone instance. To elaborate, the axial piston pump may include a swashplate that interacts with pistons and cylinders to alter the pump'sdisplacement via a change in swivel angle, in one specific example.However, other suitable types of variable displacement bi-directionalpumps have been contemplated.

The hydraulic motor 134 may be a fixed displacement bi-directional motor(e.g., fixed bent axis motor). The fixed bent axis motor is relativelycompact when compared to variable displacement motors. The system cantherefore achieve greater space efficiency and pose less spaceconstraints on other systems in the vehicle, if desired. However,alternate types of pumps and/or motors may be used, if motoradjustability is favored at the expense of compactness, for instance.

Hydraulic lines 144, 146 are attached to hydraulic interfaces in each ofthe motor and pump to enable the hydrostatic assembly to provideadditive and power circulation functionality with regard to themechanical branches arranged in parallel with the hydrostatic assembly130. For example, in an additive power mode, power from both thehydrostatic and mechanical assemblies is combined at one of theplanetary gear sets and delivered to the transmission output. Therefore,the hydraulic pump 136 and the motor 134 may be operated to flow powerto the sun gears of either planetary assembly from the hydraulic motor.In a recirculating power mode, power is recirculated through thehydrostatic assembly. Therefore, in the recirculating power mode, powerflows from the hydrostatic assembly to the shaft 120.

The transmission system 100 further includes the first planetary gearset 148 and the second planetary gear set 150. The first planetary gearset 148 may include a carrier 152 on which planet gears 154 rotate. Theplanet gears 154 may mesh with a sun gear 156 and the ring gear 158.Likewise, the second planetary gear set 150 may include the carrier 160,planet gears 162, a sun gear 164, and a ring gear 166. Therefore, thesecond planetary gear set 150 may again be a simple planetary gear set.Further, bearings arranged between the planet gears and the carrier ineach planetary arrangement may facilitate rotation thereof. The sungears and/or shafts to which they are attached may further have bearingscoupled thereto. The bearings may be roller bearings (e.g., needleroller bearings), ball bearings, or other suitable types of bearingsthat enable component rotation while constraining other relative motion.

The carrier 160 of the second planetary gear set 150 may be rotationallycoupled to the ring gear 158 of the first planetary gear set 148.Further, the carrier 160 of the second planetary gear set 150 may berotationally coupled to a shaft 167. The shaft 167 may extend through acentral opening in an extension 186, described in greater detail herein.This rotational attachment scheme may be conceptually described as aformation of mechanical branches attached in parallel to the hydrostaticassembly 130.

As described herein a parallel attachment between components,assemblies, etc., denotes that the input and output of the twocomponents or grouping of components are rotationally coupled to oneanother. This parallel arrangement allows power to recirculate throughthe hydrostatic assembly, during some conditions, or be additivelycombined from the mechanical and hydrostatic branches, during otherconditions. As a result, the transmission's adaptability is increased,which allows gains in operating efficiency to be realized, when comparedto purely hydrostatic transmissions.

The sun gears 156, 164 of the first and second planetary gear sets 148,150 may be rotationally coupled (e.g., directly attached) to oneanother. Attaching the sun gears in this manner may enable thetransmission to achieve a desired gear ratio, compactness, andefficiency.

The hydraulic motor 134 may be rotationally coupled to the sun gear 156via a mechanical bushing 168, for instance. The transmission system 100further includes a reverse clutch 170, a first forward drive clutch 172,and a second forward drive clutch 174. More generally, the first forwarddrive clutch may be referred to as a first clutch or a first forwardclutch, the reverse drive clutch may be referred to as a second clutchor a reverse clutch and the second forward drive clutch may be referredto as a third clutch or a second forward clutch. The clutches 170, 172,174 may be positioned near to an output shaft 171 and downstream of theplanetary assembly. Arranging the clutches in this location allows adesired compromise between clutch size and clutch speed. For instance,relatively high clutch speeds may generate higher power losses. Further,the reverse clutch 170 and the first forward drive clutch 172 may bearranged adjacent and coaxial to one another. In one particular example,the clutches may have a similar design to reduce manufacturingcomplexity. This twin clutch arrangement therefore permits manufacturingcosts to be reduced and increases the transmission's compactness.

The clutches 170, 172, 174 may be friction clutches that each includetwo sets of plates. The clutch plates may rotate about a common axis andare designed to engage and disengage one another to facilitate selectivepower transfer to downstream components. In this way, the clutches maybe closed and opened to place them in engaged and disengaged states. Inthe disengaged state, power does not pass through the clutch. Converselyin the engaged state, power travels through the clutch duringtransmission operation. Further, the clutches may be hydraulically,electromagnetically, and/or pneumatically actuated. For instance, theclutches may be adjusted via a hydraulic piston. The adjustability maybe continuous, in one example, where the clutch may transition throughpartially engaged states to a fully engaged state, where a relativelysmall amount of power loss occurs in the clutch. However, in otherexamples, the clutches may be discretely adjusted.

The carrier 152 may include an extension 175 with a gear 176 that mesheswith a gear 177. The gear 177, in the illustrated example, isrotationally coupled to the reverse clutch 170 and the first forwardclutch 172. The reverse clutch 170 and the first forward clutch 172 areshown arranged adjacent to one another and may share a common rotationalaxis. Because of this proximal clutch arrangement, the system mayexhibit greater compactness which poses less space constraints onadjoining vehicle systems. Alternatively, the reverse clutch may bespaced away from the first forward clutch which may, however, decreasesystem compactness.

A gear 179 may reside on an output shaft 180 of the reverse clutch 170.Likewise, a gear 181 may reside on an output shaft 182 of the firstforward clutch 172. Both gears 179, 181 may be rotationally attached tothe system output shaft 171 via gears 183, 184 respectively. In thisway, both the reverse clutch and the first forward clutch deliver powerto the transmission's output, during different operating conditions.

The system output shaft 171 may include one or more interfaces 185(e.g., yokes, gears, chains, combinations thereof, etc.). The outputshaft is specifically illustrated with two outputs. However, thetransmission may include an alternate numbers of outputs. The gear 179is rotationally coupled to the output shaft via meshing with gear 183.Arrows 191 depict the flow of power from the transmission system todrive axles 192 and/or other suitable downstream vehicle components orvice versa. A driveline with a shaft, joints, and the like may be usedto carry out the power transfer between the transmission and the axles.It will be understood that the drive axles may be coupled to drivewheels.

The ring gear 166 of the second planetary gear set 150 may include theextension 186 with a gear 187 position thereon. The gear 187 may berotationally attached to a gear 188 in the second forward clutch 174, asindicated via a dashed line. The gear 188 may be coupled to a first setof plates in the clutch 174. A second set of plates in the clutch may beattached to an output shaft 189 and a gear 190. The gear 190 may berotationally coupled to the gear 183, as indicated by a dashed line. Dueto the aforementioned arrangement of the clutches and the planetary gearsets, the transmission system 100 achieves a higher efficiency andenhanced drivability, comfort, and productivity than previoushydromechanical transmissions.

The transmission system 100 may additionally include a lubricationsystem which may include a sump, as previously discussed. Thislubrication system may further include conventional components forlubricating the gears and/or the clutches such as pumps, conduits,valves, and the like.

A control system 193 with a controller 194 may further be incorporatedin the transmission system 100. The controller 194 includes a processor195 and memory 196. The memory 196 may hold instructions stored thereinthat when executed by the processor cause the controller 194 to performthe various methods, control strategies, etc., described herein. Theprocessor 195 may include a microprocessor unit and/or other types ofcircuits. The memory 196 may include known data storage mediums such asrandom access memory, read only memory, keep alive memory, combinationsthereof, and the like.

The controller 194 may receive vehicle data and various signals fromsensors positioned in different locations in the transmission system 100and/or the vehicle 102. The sensors may include gear speed sensors 197,198, 199 which detect the speed of gear 116, gear 184, and gear 176,respectively. In this way, gear speed at the input and the output of thesystem may be detected along with the gear speed at the output of thefirst planetary gear set 148. However, in other examples, the speeds ofat least a portion of the gears may be modeled by the controller.

The controller 194 may send control signals to an actuator in thehydraulic pump 136 or an actuation system coupled to the pump to adjustthe pumps output and/or direction of hydraulic fluid flow. Additionally,the clutches 170, 172, 174 may receive commands (e.g., opening orclosing commands) from the controller and actuators in the clutches oractuation systems coupled to the clutches may adjust the state of theclutch in response to receiving the command. For instance, the clutchesmay be actuated via hydraulically controlled pistons, although othersuitable clutch actuators have been envisioned. The other controllablecomponents in the transmissions system include the hydraulic motor 134,the motive power source 104, and the like. These controllable componentsmay function similarly with regard to receiving control commands andadjusting an output and/or a state of a component responsive toreceiving the command via an actuator. Additionally or alternatively, avehicle electronic control unit (ECU) may be provided in the vehicle tocontrol the power source (e.g., engine and/or motor). Furthermore, thecontrol system 193 and specifically the controller 194 with the memory196 and processor 195 may be configured to carry out the shiftingmethods elaborated upon herein with regard to FIGS. 3-8 and 13.

The transmission system 100 may include an input device 151 (e.g., anaccelerator pedal, a control-stick, levers, buttons, combinationsthereof, and the like). The input device 151, responsive to driverinput, may generate a transmission speed or torque adjustment requestand a desired drive direction (a forward or reverse drive direction).Further, the transmission system may automatically switch between drivemodes when demanded. To elaborate, the operator may request a forward orreverse drive mode speed or torque change, and the transmission mayincrease speed or torque and automatically transition between the driveranges associated with the different drive modes, when needed. Further,in one example, the operate may request reverse drive operation whilethe vehicle is operating in a forward drive mode. In such an example,the transmission may automatically initiate a shift (e.g., synchronousshift) between the forward and reverse drive modes. In this way, theoperator may more efficiently control the vehicle, in comparison totransmissions designed for manual drive mode adjustment. However, inother examples, the system may be designed to allow the vehicle operatorto manually request a mode change between the forward drive ranges, forinstance. It will further be appreciated that the power source may becontrolled in tandem with the transmission. For instance, when a speedadjustment requested is received by the controller, the power source'soutput speed may be correspondingly increased.

FIG. 2 shows an illustration of a transmission system 200 using a wolfsymbol scheme. In the wolf scheme, lines represent shafts, gears, and/orother mechanisms for rotational energy transfer. Further in the wolfscheme, circles represent planetary gear sets and boxes representnon-planetary gear sets which may include shafts, gears, and the like.Each gear set may have an associated ratio. Further, in the wolf schemeclutches are represented via parallel lines and junctions where power iscombined from multiple branches are represented via solid dots. Thejunctions may include gears, shafts, shaft sections, and the like. Thetransmission system 200 shown in FIG. 2 is an example of thetransmission system 100 shown in FIG. 1. Because of this correspondence,these transmission systems may share common functional and structuralfeatures. Repeated description is therefore omitted for concision.

The transmission system 200 may include an internal combustion engine202 or other suitable motive power source (e.g., electric motor ormotor-generator). A first junction 204 rotationally couples twomechanical branches 206, 208 to a hydrostatic branch 210 with thehydrostatic assembly 212. The first mechanical branch 206 may berotationally attached to a ring gear 214 in a first planetary gear set216. Conversely, the second mechanical branch 208 may be rotationallyattached to a carrier 218 in a second planetary gear set 220.

The hydrostatic assembly 212 includes a hydraulic pump 222 and ahydraulic motor 224. Further, a gear set 226 may be arranged in thehydrostatic branch between the pump 222 and the engine 202. The gear 226may be rotationally coupled to a mechanical interface 227 of the pump222. Hydraulic interfaces 228 in each of the pump and the motor may bein fluidic communication via conduits 230. A mechanical interface 227 ofthe pump may be mechanically attached to the gear set 226. Further, amechanical interface 234 of the motor may be mechanically attached to asecond junction 236. The second junction 236 serves as a rotationalconnection between sun gears 238, 240 of the first and second planetarygear sets 216, 220.

The transmission system 200 again may include a reverse clutch 242, afirst forward clutch 244, and a second forward clutch 246. Theseclutches are mechanically coupled in parallel to allow one of theclutches to be engaged while the others are disengaged in the differentdrive ranges. In this way, each clutch corresponds to a different driverange.

A gear set 248 may be rotationally coupled to a carrier 250 of the firstplanetary gear set 216. The gear sets shown in FIG. 2 may include twogears. A junction 252 may serve as a mechanical connection between thegear set 248 and the clutches 242, 244. Further, a gear set 254 may berotationally coupled to the reverse clutch 242 and a gear set 256 iscoupled to the first forward clutch 244. Another junction 258 may serveto rejoin the mechanical branches associated with the reverse clutch andthe first forward clutch. A ring gear 262 of the second planetary gearset 220 may be rotationally coupled to the gear set 260. Further, a gearset 263 may be coupled to the second forward clutch 246 and a junction264. The junction 264 may function as an output for the three clutchbranches.

FIGS. 3-8 depict power paths through the transmission system 200 indifferent drive ranges. Arrows with cross-hatching depict a circulatingpower flow in which the power path travels to back to upstreamcomponents. Conversely, arrows without cross-hatching depict adownstream power flow towards the transmission output.

Turning specifically to FIG. 3, showing the transmission systemoperating in a first stage of the first drive range. In the first driverange, the first forward drive clutch 244 is engaged and the reversedrive clutch 242 and the second forward drive clutch 246 are disengaged.As such, in the first drive range the transmission is in an inputcoupled power split mode.

In this power split mode, arrows 300 indicate the path of power from theengine 202 to the junction 204, from the junction 204 to the firstmechanical branch 206, and from the first mechanical branch to the ringgear 214 of the first planetary gear set 216. Arrows 302 indicate therecirculation of power from the sun gear 238 of the first planetary gearset 216 to the hydraulic motor 224, from the hydraulic motor to thehydraulic pump 222, from the hydraulic pump to the gear set 226, andfrom the gear set to the junction 204. Arrows 304 indicate the powerpath from the carrier 250 of the first planetary gear set 216 to thegear set 248, from the gear set 248 to the first forward drive clutch244 via the junction 252, from the first forward drive clutch to thegear set 256, and from the gear set 256 to the transmission's output306. In this way, a portion of the power is circulated back through thehydrostatic assembly 212 while another portion is transferred throughthe clutch to the output. Due to the circulation of the power throughthe hydrostatic assembly, the transmission may be operated with arelatively high efficiency when compared to solely mechanical orhydrostatic transmissions.

In a second stage of the first drive gear range, the hydraulic powerpath changes directions. During this directional change, the power inthe hydraulic path crosses zero and goes to additive power of mechanicaland hydraulic paths, as shown in FIG. 4.

In the second stage of the first drive range, the power path travelsthrough the first mechanical branch 206 and the hydrostatic assembly 212in parallel. Further, in the second stage of the first drive range,power from the mechanical and hydrostatic branches are additivelycombined at the first planetary gear set 216 and then transferredthrough the first forward clutch 244 to the transmission output 306.Specifically, as illustrated in FIG. 4, arrows 400 indicate the powerpath through the mechanical branch 206 to the ring gear 214 of the firstplanetary gear set 216. Further, arrows 402 indicate the power paththrough the hydrostatic branch (the gear set 226, the hydraulic pump222, and the hydraulic motor 224) to the sun gear 238 of the firstplanetary gear set 216. Further, arrows 404 indicate the power path fromthe carrier 250 of the first planetary gear set 216 to the gear set 248,from the gear set to the first forward clutch 244, from the firstforward clutch to the gear set 256, and from the gear set to the output306.

When the ring gear speed of the second planetary gear set 220 allowssynchronization of the second forward clutch 246, the drive range ischanged (e.g., transitioned from the first to the second drive range) byopening the first drive clutch 244 and closing the second drive clutch246 via a synchronous shift, for example. Closing a friction clutchinvolves the frictional engagement of sets of plates in the clutch totransfer power between the clutch's input and output. Conversely,opening a friction clutch involves frictional disengagement of the setsof plates in the clutch to decouple the clutch's input from the output.Further, a synchronous shift includes concurrently opening one clutchwhile closing another.

FIG. 5 correspondingly shows the transmission system 200 operating in afirst stage of the second forward drive range. In the second forwarddrive range, the transmission works similarly to the first forward driverange but with a different mechanical path ratio. In the second range,the reverse clutch 242 and the first forward clutch 244 are eachdisengaged, and the second forward clutch 246 is engaged.

In the first stage, power is circulated back through the hydrostaticassembly 212 to the second mechanical branch 208. Arrows 500specifically indicate the power path from the sun gear 240 of the secondplanetary gear set 220 to the hydrostatic assembly 212. Arrows 500further indicate power path through the hydrostatic assembly 212 to thegear set 226. The power path through the hydrostatic assembly involvesthe transfer of power through the hydraulic motor 224 and hydraulic pump222. The power path from the junction 204, through the second mechanicalbranch 208, and to the carrier 218 of the second planetary gear set 220is indicated via arrows 502. Further, arrows 504 indicate the power pathfrom the ring gear 262 to the gear set 260, and through the secondforward clutch 246 as well as the gear set 263 to the output 306.

FIG. 6 shows the transmission system 200 operating in a second stage ofthe second forward drive range after the power flow in the hydraulicpath has changed direction (switching from circulating power, crossingzero power of the hydrostatic path, and transitioning to an additivepower flow of the mechanical and hydraulic branches). In this way, theratio in the second forward drive range may be continuously adjustedacross the range in an efficient manner.

Arrows 600 embody the power path from the junction 204 through the gearset 226 as well as the hydrostatic assembly 212 to the sun gear 240 ofthe second planetary gear set 220. Arrows 602 indicate the power pathfrom the junction 204, through the second mechanical branch 208, and tothe carrier 218 of the second planetary gear set 220. Additionally,arrows 604 indicate the power path from the ring gear 262 of the secondplanetary gear set 220, through the gear set 260, second forward clutch246 as well as the gear set 263, and to the transmission output 306.

FIGS. 7 and 8 illustrate a first and second stage of the reverse driverange. The reverse range is similar to the first forward drive range,only that the transmission ratio in the mechanical path through the gearset 254 inverts the output speed direction. In the reverse drive range,the reverse clutch is engaged and the first and second forward clutchesare disengaged. FIG. 7 specifically depicts arrows 700 which embody apower path from the junction 204, through the first mechanical branch206, and to the ring gear 214 in the first planetary gear set 216.Arrows 702 embody the power path that circulates through the hydrostaticassembly 212 and the gear set 226. Further, arrows 704 indicate thepower path from the carrier 250 of the first planetary gear set 216,through the gear set 248, the reverse clutch 242, as well as the gearset 254, and to the transmission output 306.

Again, during the reverse drive range, power flow in the hydraulic pathchanges direction (switching from a power circulation configuration,crossing zero power of the hydrostatic path, and transitioning to anadditive power flow configuration, indicated in FIG. 8). Arrows 800 inFIG. 8 indicate the power path which travels through the firstmechanical branch 206 and to the ring gear 214 of the first planetarygear set 216. Arrows 802 indicate the power path through the hydrostaticassembly 212 to the sun gear 238 of the first planetary gear set 216.After the power is additively combined in the first planetary gear set,power travels from the carrier 250 to the output 306 via the reverseclutch 242, as indicated via arrows 804.

FIG. 9 shows a chart 900 that illustrates the configurations (engaged ordisengaged) of the clutches 242, 244, 246, shown in FIGS. 2-8 in thedifferent drive modes (a reverse drive range, a first forward driverange, and second forward drive range). In the reverse drive range, thereverse clutch 242 is engaged while the clutches 244, 246 aredisengaged. Additionally, in the first forward drive range, the firstforward clutch 244 is engaged while the clutches 242, 246 are disengagedand in the second forward drive range, the second forward clutch 246 isengaged while the clutches 242, 244 are disengaged. To smoothly andefficiently transition between the different drive modes, the clutchesmay be synchronously shifted, as previously mentioned.

FIG. 10 shows a plot 1000 with the hydrostatic ratio represented on theordinate and the transmission ratio represented on the abscissa. Theseratios are examples of ratios that may be generated by the transmissionsystems described above with regard to FIGS. 1-9. To elaborate, theordinate and abscissa indicate zero values of the other correspondingratios. As such, points below the abscissa represent negativehydrostatic ratios and points above the abscissa represent positivehydrostatic ratios. Points to the left of the ordinate representnegative transmission ratios and points to the right of the ordinaterepresent positive transmission ratios. Further, the different driveranges (a reverse drive range, a first forward drive range, and a secondforward drive range) for the transmissions operating modes aredemarcated. However, other transmission embodiments may have alternatecorrespondence between the hydrostatic ratio and the transmission ratio.

In the reverse drive range, power is recirculated through thehydrostatic assembly in a first portion of the range. Conversely, in asecond portion of the range, power is additively combined from themechanical branch and the hydrostatic branch. Transmission ratio value−tr1 indicates the boundary between the first and second portions of thereverse drive range.

At 1002, a shift (e.g., synchronous shift) occurs between the reverseclutch and first forward clutch and the transmission enters the firstforward drive range or vice versa. In a first part of this drive range,power is recirculated through the hydrostatic assembly, similar to thereverse drive range. However, in the first forward drive range, thetransmission's output is rotating in an opposite direction when comparedto the reverse drive range. In a second portion of the first forwarddrive range, power from the hydrostatic assembly and the mechanicalassembly is additively combined at the first planetary gear assembly.Transmission ratio value trl denotes the boundary between the first andsecond portions (recirculation and additive power arrangements) of thefirst forward drive range.

At 1004, a shift (e.g., synchronous shift) occurs between the firstforward clutch and the second forward clutch or vice versa. In a firstportion of the second forward drive range, power is recirculated throughthe hydrostatic assembly from the second planetary gear set. Conversely,in a second portion of the second forward drive range, power from thesecond mechanical branch and the hydrostatic assembly is additivelycombined at the second planetary gear set.

FIGS. 11-12 show pump swivel angle diagrams with sequential control.These diagrams serve as examples of swivel angle adjustments that may beimplemented via the hydraulic pump in the transmission systems,described above with regard to FIGS. 1-9. When a fixed bent axis motoris used in the transmission, the swivel angle may be equivalent to thehydrostatic ratio, illustrated in FIG. 10. To elaborate, plots 1100,1200 with a pump swivel angle on the ordinate and a hydrostatic ratio onthe abscissa are illustrated in FIGS. 11-12, respectively. Zero swivelangle and hydrostatic ratio values are indicated on both of the ordinateand abscissa. Although specific swivel angle and hydrostatic ratiovalues are not indicated, negative and positive swivel angles (α) areratios (r) are provided for reference.

FIG. 11 illustrates the pump swivel angle for the forward drive mode. Inthe forward drive mode, the pump swivel angle reaches a maximum value(α2) and then decreases as the hydrostatic ratio increases. On the otherhand, FIG. 12 illustrates the pump swivel angle in the reverse drivemode. In the reverse drive mode, as pump swivel angle increases thehydrostatic ratio decreases until ratio −r1 is reached. As such, thepump swivel angle may be adjusted to alter the ratio of the hydrostaticbranch in the different drive modes.

FIG. 13 shows a method 1300 for operation of a hydromechanicaltransmission. The method 1300 may be carried out by the hydromechanicaltransmissions and components described above with regard to FIGS. 1-9,in one example. However, in other examples, the method 1300 may beimplemented using other suitable hydromechanical transmissions andcorresponding components. Further, the method may be carried out asinstructions stored in non-transitory memory executed by a processor ina controller. As such, performing the method steps may include sendingand/or receiving commands which trigger adjustment of associatecomponents, as previously indicated.

At 1302, the method includes determining operating conditions. Theoperating conditions may include transmission speed, transmissiontorque, vehicle speed, operator torque request, operator speed request,ambient temperature, transmission temperature, and the like. Theseoperating conditions may be determined using sensor data and/or modelingalgorithms.

At 1304, the method includes determining if a torque or a speedadjustment request has been received. For example, a torque or a speedadjustment request may be generated in response to operator interactionwith an input device such as an accelerator pedal, a control stick, alever, and the like.

If a torque or speed adjustment request has not been received (NO at1304) the method proceeds to 1306 where the method includes sustainingthe current transmission control strategy. For instance, thetransmission may be operated at a torque set-point, or a speed set-pointin some cases, within one of the drive ranges.

If a torque or speed adjustment request has been received (YES at 1304)the method advances to 1308. At 1308, the method judges whether or notto change drive modes. To elaborate, the transmission may be designed toimplement two points of speed ratio synchronization of two of theclutches. The first point synchronizes the first forward clutch (e.g.,clutch 172, shown in FIG. 1) and the second forward clutch (e.g., clutch174, shown in FIG. 1) and the second point synchronizes the firstforward clutch and the reverse clutch (e.g., clutch 170, shown in FIG.1). The instructions in the transmission's controller may be designed tocontrol the torque provided by the transmission to the output shaft.Therefore, the transmission's speed ratio may be a consequence of thetorque applied by the transmission. For example, while the engine isoperating at a substantially constant speed, if a higher pulling torqueis applied by the transmission on the output shaft a higher output shaftacceleration and consequently a higher speed ratio gradient occur. Thetransmission's speed ratio may be altered as a consequence of anoperator torque adjustment request. At a certain point of theacceleration, the transmission's speed ratio will approach a maximumvalue possible within the current operating drive range. As such, whenthe maximum speed value is approached, the operating drive range may bechanged to prevent interruption of the pulling torque continuity to thewheel. For instance, the transmission may be transitioned from thereverse drive range to the first forward drive range or from the firstforward drive range to the second forward drive range. Conversely, whenthe transmission's actual speed ratio approaches a minimum value of theoperating drive range, the transmission may also change the operatingdrive range. For example, the transmission may transition from thesecond forward drive range to the first forward drive range or from thefirst forward drive range to the reverse drive range. Therefore, in suchan example, a mode change operation may be implemented where thetransmission (e.g., synchronously transitions) from the first forwarddrive range to the second forward drive range. However, if the torque orspeed adjustment request can be handled in the current operational driverange, a drive mode change may be temporarily inhibited.

If it is determined that a mode change should not be carried out (NO at1308), the method moves to 1310. At 1310, the method includes operatingthe transmission in one of the drive ranges to adjust transmissionoutput torque. For example, the hydrostatic assembly may be adjusted toalter the transmission's output torque, in one example, or speed, inanother example.

Operating the transmission in one of the drive ranges may include either1312 or 1314 or transitioning between block 1312 and 1314 or vice versa.At 1312, the method may include additively combining power from one ofthe mechanical branches in the mechanical assembly and the hydrostaticassembly through one of the planetary gear sets. In this way, power maybe efficiently combined in the transmission to achieve a target speed ortorque.

At 1314, the method may include recirculating power through thehydrostatic assembly while transferring a portion of the power from oneof the mechanical branches in the mechanical assembly through one of theplanetary gear sets to the transmission output.

If, however, it is judged that a mode change request should be carriedout (YES at 1308), the method proceeds to 1316. In one example, a shiftcommand may be generated (e.g., automatically generated) when it isdetermined a mode change request should be implemented. The shiftrequest may therefore be a request to shift between the reverse driverange and the first forward drive range or the first forward drive rangeand the second forward drive range or vice versa. At 1316, the methodincludes transitioning between two of the drive ranges. This transition,which may be referred to as a shifting transient, may include step 1318.At 1318, the method includes, synchronizing operation of two of theclutches to transition between two of the drive ranges. For instance,the reverse clutch may be disengaged while the first forward clutch isengaged or vice versa. In another example, the first forward clutch maybe disengaged while the second forward clutch is engaged while theoutput shaft torque remains at a desired value or vice versa. In thisway, the transmission operating drive range may be changed to preventinterruption of the pulling torque continuity to the wheels.Consequently, the transmission performance is increased, therebyincreasing customer satisfaction. It will be understood, that thetransmission drive mode transitions may be carried out automatically.That is to say, the drive modes may be switched between based on thetransmission's speed ratio rather than an explicit request to shiftbetween drive modes via operator interaction with a gear selector.

Method 1300 allows transmission torque adjustments to be smoothly andefficiently carried out. As a results, the operating efficiency of thevehicle using the transmission is increased and transmission longevitymay be correspondingly increased, in some cases. Thus, method 1300enables transmission performance to be enhanced.

FIG. 14 illustrates a prophetic use-case power limit curve 1400. Thepower limit curve may correspond to one use-case embodiment, of thepreviously described hydromechanical transmissions. Torque isrepresented on the ordinate while speed is represented on the abscissa.To elaborate, the ordinate is a zero speed value and the abscissa is azero torque value. As such, negative speed values are located to theleft of the ordinate and positive speed values are located to the rightof the ordinate. Further, positive torque values are located above theabscissa and negative torque values are located below the abscissa.

As shown in FIG. 14, the maximum torque in the first forward drive rangemay be greater than the maximum torque in the reverse drive range.Further, the maximum speed in the reverse drive range may be −2000 RPMand the maximum speed in the second forward drive range may be 3700 RPM.In this way, the transmission's maximum output speeds may be asymmetricfor forward and reverse directions. However, numerous suitable maximumtorque and speed values have been contemplated. The transmission's powerlimit curve may be selected based on end-use vehicle design parameterssuch as vehicle weight, expected PTO loads, expected vehicle loads, andthe like.

In another prophetic use-case embodiment, the transmission may provide100% tractive effort at 1500 RPM and 40% tractive effort at 900 RPM.This may allow the transmission to fulfill load spectrums that thetransmission may be anticipated to experience in several intendedoperating environments. However, other transmission embodiments may havetractive efforts mapped to different speeds and this correlation may beset based on a variety of factors such as expected transmission loads,transmission operating efficiency, and the like.

FIG. 15 shows a prophetic use-case plot 1500 of transmission speed ratiovs. time and a plot 1502 of transmission pulling torque vs. time. Thus,speed ratio and pulling torque are on the ordinates for plots 1500, 1502and time is on the abscissas. The pulling torque may be a controlledvariable. As previously discussed, when the transmission's speed ratioapproaches a threshold value rl, a drive range transition may beinitiated. The threshold value rl may specifically correspond to amaximum value possible within the current drive range. As such, thetransmission may transition between the first drive range and the seconddrive range when the maximum value is approached. However, in otherexamples, when the speed ratio is decreasing, the threshold value maycorrespond to a minimum value that is possible within the current driverange. Therefore, in such an example, when the minimum speed ratio valueis reached, the transmission may transition from the second drive rangeto the first drive range or from the first drive range to the reversedrive range. Returning to the example, depicted in FIG. 15, whentransitioning from the first drive range to the second drive range, thefirst forward drive clutch may be synchronized with the second forwarddrive clutch. Synchronization of the clutches may include decreasing thetorque transfer through the first forward clutch while correspondinglyincreasing torque transfer through the second forward clutch to maintaina desired transmission output torque.

FIG. 16 shows prophetic use-case plots 1600, 1602 of clutch differentialspeeds vs. time. Thus, the clutch differential speed is on the ordinateand time is on the abscissa. Plot 1600 specifically corresponds to thedifferential speed with regard to first forward drive clutch, and plot1602 corresponds to the differential speed with regard to the secondforward drive clutch. FIG. 16 further shows prophetic use-case plots1604, 1606 of clutch pressures vs. time. Thus, clutch pressure is on theordinate and time is on the abscissa. Plot 1604 specifically correspondsto the first forward drive clutch and plot 1606 corresponds to thesecond forward drive clutch. As shown, the differential speed of thefirst forward drive clutch remains at zero until t1, after which itincreases. Conversely, the differential speed of the second forwarddrive clutch decreases until it reaches zero at t1, after which thedifferential speed remains zero. Correspondingly, the pressure deliveredto the first forward clutch is decreased until t1, and the pressuredelivered to the second forward clutch is adjusted to induce clutchengagement. For instance, the pressure delivered to the second forwarddrive clutch may be adjusted to move the clutch through a filling phaseand into a clutch modulation phase where the clutch moves towards fullengagement.

The sum of the torque transferred by each of the two clutches involvedin the gear shift (e.g., the first forward drive clutch and the secondforward drive clutch, in the illustrated example) allows thetransmission to maintain a desired output shaft torque. In this way,transmission performance may be enhanced via a reduction in torqueinterruptions that occur during shifting transients in comparison tocertain prior types of multi-speed transmissions.

FIG. 17 shows a prophetic use-case plot 1700 of the hydrostatic motortorque vs. time. Thus, hydrostatic motor torque is on the ordinate andtime is on the abscissa. FIG. 17 further shows prophetic use-case plots1702, 1704 of clutch pressure vs. time. Therefore, clutch pressure in onthe ordinate and time is on the abscissa. Plot 1702 specificallycorresponds to the pressure of the first forward clutch and plot 1704corresponds to the pressure of the second forward clutch. As shown, inFIG. 17 the hydrostatic motor torque decreases below a null value duringthe transition from the first drive mode to the second drive mode. Toelaborate, the hydrostatic motor torque set-point may be calculatedbased on the amount of torque transferred through the two clutches thatare involved in the drive mode transition. Determining the hydrostaticmotor torque set-point in this manner enables the second forward clutch,which is being engaged, to reach synchronization with the first forwarddrive clutch. Further, the hydrostatic unit may be a “slave” of theclutches during the gear shift event. In other words, during a gearshift, the hydrostatic unit may be controlled based on the engagementand disengagement of the clutches during the shift.

FIG. 18 shows the transmission system 100 operating to shift into thereverse range. To elaborate, torque of the hydraulic motor 134 in thehydrostatic assembly 130, reverse clutch 170, first forward drive clutch172, and the output shaft 171 are indicated by arrows 1800, 1802, 1804,1806, respectively. During the reverse shift operation, the hydrostaticmotor torque may work in the same direction of the torques of theclutches to enable the incoming clutch (i.e., the clutch which begins totransition into a fully engaged configuration) to be synchronized.Equation (1) may therefore represent the relationship of the motor andclutch torques where a and b are mechanical gains, C1 torque is thetorque of the first forward drive clutch, and C2 torque is the torque ofthe second forward drive clutch.Motor torque=a*(C1 torque)+b*(C2 torque)  (1)

Further, the clutches may enable a desired torque to be applied to theoutput shaft. Equation (2) may represent the relationship between outputtorque and the torques of the clutches where output torque is the torqueof the output shaft, c and d are mechanical gains, C1 torque is thetorque of the first forward drive clutch, and C2 torque is the torque ofthe second forward drive clutch.Output torque=c*(C1 torque)+d*(C2 torque)  (2)

Synchronizing the clutches in this manner permits torque interruptionsduring shifting transients to be substantially avoided, if desired.Consequently, shifting performance may be enhanced and transmissionefficiency may be increased.

The technical effect of the hydromechanical transmissions andtransmission operating methods described herein is to provide a targetedgroup of drive ranges in an energy and space efficient package. Further,the transmission systems and methods described herein allow thetransmission to smoothly transition between different drive ranges witha decreased amount (e.g., substantially zero) power interruption,thereby decreasing NVH during mode shifting transients and furtherincreasing transmission energy efficiency.

FIGS. 1-8 and 18 show example configurations with relative positioningof the various components. If shown directly contacting each other, ordirectly coupled, then such elements may be referred to as directlycontacting or directly coupled, respectively, at least in one example.Similarly, elements shown contiguous or adjacent to one another may becontiguous or adjacent to each other, respectively, at least in oneexample. As an example, components laying in face-sharing contact witheach other may be referred to as in face-sharing contact. As anotherexample, elements positioned apart from each other with only a spacethere-between and no other components may be referred to as such, in atleast one example. As yet another example, elements shown above/belowone another, at opposite sides to one another, or to the left/right ofone another may be referred to as such, relative to one another.Further, as shown in the figures, a topmost element or point of elementmay be referred to as a “top” of the component and a bottommost elementor point of the element may be referred to as a “bottom” of thecomponent, in at least one example. As used herein, top/bottom,upper/lower, above/below, may be relative to a vertical axis of thefigures and used to describe positioning of elements of the figuresrelative to one another. As such, elements shown above other elementsare positioned vertically above the other elements, in one example. Asyet another example, shapes of the elements depicted within the figuresmay be referred to as having those shapes (e.g., such as being circular,straight, planar, curved, rounded, chamfered, angled, or the like).Additionally, elements co-axial with one another may be referred to assuch, in one example. Further, elements shown intersecting one anothermay be referred to as intersecting elements or intersecting one another,in at least one example. Further still, an element shown within anotherelement or shown outside of another element may be referred as such, inone example. In other examples, elements offset from one another may bereferred to as such.

The invention will be further described in the following paragraphs. Inone aspect, a transmission system is provided that comprises a hydraulicpump and a hydraulic motor rotationally coupled in parallel with a firstplanetary gear set and a second planetary gear set; wherein sun gears ofthe first and second planetary gear sets are rotationally coupled to thehydraulic motor; and wherein a carrier of the first planetary gear setis rotationally coupled to a first clutch and a second clutch; andwherein a ring gear of the second planetary gear set is rotationallycoupled to a third clutch.

In another aspect, a hydromechanical variable transmission is providedthat comprises a hydraulic pump and a hydraulic motor rotationallycoupled in parallel with a first planetary gear set and a secondplanetary gear set; wherein sun gears of the first and second planetarygear sets are rotationally coupled to the hydraulic motor; wherein acarrier of the first planetary gear set is rotationally coupled to afirst forward clutch and a reverse clutch; and wherein a ring gear ofthe second planetary gear set is rotationally coupled to a secondforward clutch.

In another aspect, a power split transmission is provided that comprisesa hydraulic pump and a hydraulic motor rotationally coupled in parallelwith a first planetary gear set and a second planetary gear set; whereinsun gears of the first and second planetary gear sets are rotationallycoupled to the hydraulic motor; wherein a carrier of the first planetarygear set is rotationally coupled to a first forward clutch and a reverseclutch; and wherein a ring gear of the second planetary gear set isrotationally coupled to a second forward clutch.

In yet another aspect, a transmission system is provided that comprisesa hydrostatic assembly and a mechanical assembly coupled in parallel viaa first planetary gear set and a second planetary gear set; a pluralityof clutches coupled in parallel to a transmission output, comprising: afirst clutch rotationally coupled to a carrier of the first planetarygear set; a second clutch rotationally coupled to the carrier inparallel with the first clutch; and a third clutch rotationally coupledto a ring gear of the second planetary gear set; a controller includinginstructions stored in non-transitory memory that when executed by aprocessor, responsive to receiving a speed or a torque change request,cause the controller to: operate the first, second, and/or thirdclutches to transition between two drive ranges in a group of driveranges, wherein the group of drive ranges includes at least one reversedrive range and two forward drive ranges.

In another aspect, a method for operation of a transmission system, thatcomprises transitioning between an engaged state and a disengaged stateof one or more of a reverse clutch, a first forward clutch, and a secondforward clutch when switching between two drive modes in a group ofdrive modes; wherein the first forward clutch is coupled to a carrier ofa first planetary gear set, the reverse clutch is coupled to the carrierin parallel with the first forward clutch, and the second forward clutchis coupled to the ring gear of the second planetary gear set; andwherein a hydrostatic assembly, a first mechanical branch, and a secondmechanical branch are couple in parallel to the first planetary gear setand the second planetary gear set. The method may further include, inone example, operating the transmission system in one of the drive modesand, while operating in the one of the drive modes, delivering powerfrom the first or the second planetary gear set to a mechanical assemblyof the transmission system, wherein the mechanical assembly is arrangedparallel to the hydrostatic assembly.

In yet another aspect, a hydromechanical variable transmission isprovided that comprises a hydrostatic assembly and a mechanical assemblycoupled in parallel via a first and a second planetary gear set; aplurality of clutches coupled in parallel to a transmission output,comprising: a first clutch coupled to a carrier of the first planetarygear set; a second clutch coupled to the carrier in parallel with thefirst clutch; and a third clutch coupled to a ring gear of the secondplanetary gear set; and a controller including instructions stored innon-transitory memory executable by a processor, that during a shiftingtransient, cause the controller to: operate the first, second, and/orthird clutches to transition between two drive ranges in a group ofdrive ranges; wherein the group of drive ranges includes at least onereverse drive range and two forward drive ranges.

In any of the aspects or combinations of the aspects, the second clutchmay be a reverse clutch.

In any of the aspects or combinations of the aspects, the first clutchand the reverse clutch may be each directly coupled to the carrier andare adjacent to one another.

In any of the aspects or combinations of the aspects, the first, second,and third clutches may be friction clutches.

In any of the aspects or combinations of the aspects, the transmissionsystem may further comprise a mechanical power take-off (PTO)rotationally coupled to a mechanical branch that extends between a powersource and the hydraulic pump.

In any of the aspects or combinations of the aspects, the transmissionsystem may further comprise a mechanical power take-off (PTO) coupled tothe hydraulic pump.

In any of the aspects or combinations of the aspects, the hydraulicmotor may be a fixed bent axis motor.

In any of the aspects or combinations of the aspects, the hydraulic pumpmay be an axial piston pump.

In any of the aspects or combinations of the aspects, the first andsecond planetary gear sets may be coaxially arranged.

In any of the aspects or combinations of the aspects, the first andsecond clutches may be axially offset from the third clutch.

In any of the aspects or combinations of the aspects, the transmissionsystem may be included in an off-highway vehicle.

In any of the aspects or combinations of the aspects, the transmissionsystem may further include an input interface that is configured torotationally couple to a motive power source and an output interfacethat is configured to rotationally couple to one or more vehicle axlesand wherein the input interface is axially offset from the outputinterface.

In any of the aspects or combinations of the aspects, thehydromechanical variable transmission may be an infinitely variabletransmission.

In any of the aspects or combinations of the aspects, thehydromechanical variable transmission may include a mechanical powertake-off (PTO) coupled to an input shaft that receives rotational inputfrom a motive power source. In any of the aspects or combinations of theaspects, the first forward clutch and the reverse clutch may becoaxially arranged to one another and axially offset from the secondforward clutch and the first and second planetary gear sets.

In any of the aspects or combinations of the aspects, the hydraulicmotor may be a fixed bent axis motor and wherein the hydraulic pump is avariable displacement axial piston pump.

In any of the aspects or combinations of the aspects, the first forwardclutch, the reverse clutch, and the second forward clutch may be coupledin parallel with one another.

In any of the aspects or combinations of the aspects, the first forwardclutch and the reverse clutch may be coupled to a first central shaftthat is radially offset from a second central shaft that is coupled tothe second forward clutch.

In any of the aspects or combinations of the aspects, the transmissionsystem may further comprise instructions stored in the non-transitorymemory that when executed by the processor, while the transmissionsystem is operating in the reverse drive range or one of the two forwarddrive ranges, cause the controller to: operate the hydrostatic assemblyand the mechanical assembly to additively deliver power to the first orthe second planetary gear set.

In any of the aspects or combinations of the aspects, the transmissionsystem may further comprise instructions stored in the non-transitorymemory that when executed by the processor, while the transmissionsystem is operating in the reverse drive range or one of the two forwarddrive ranges, cause the controller to: operate the hydrostatic assemblyto circulate power from the first or the second planetary gear set backto the mechanical assembly.

In any of the aspects or combinations of the aspects, operating thefirst, second, and third clutches to shift between the two drive rangesmay include opening the second clutch and closing the third clutch whena ring gear in the second planetary gear set allows synchronization ofthe third clutch.

In any of the aspects or combinations of the aspects, the second clutchmay be a reverse drive clutch and the first clutch and the third clutchare forward drive clutches.

In any of the aspects or combinations of the aspects, the first, thesecond, and the third clutches may be friction clutches.

In any of the aspects or combinations of the aspects, the transitionbetween the two drive ranges may be synchronously implemented.

In any of the aspects or combinations of the aspects, the group of driveranges may include only the reverse drive range and the two forwarddrive ranges.

In any of the aspects or combinations of the aspects, transitioningbetween the engaged state and the disengaged state of one or more of thereverse clutch, the first forward clutch, and the second forward clutchmay include opening the first forward clutch and closing the secondforward clutch when a ring gear in the second planetary gear set allowssynchronization of the second forward clutch.

In any of the aspects or combinations of the aspects, transitioningbetween the two drive modes may be initiated in response to a torqueadjustment request and wherein the group of drive modes includes areverse drive range, a first forward drive range, and a second forwarddrive range.

In any of the aspects or combinations of the aspects, operating thetransmission system in one of the drive modes may include, in a portionof a drive range, operating the hydrostatic assembly to deliver power tothe first or the second planetary gear set which is additively combinedwith one of the first and second mechanical branches.

In any of the aspects or combinations of the aspects, operating thetransmission system in one of the drive modes may include transferringpower through only one of the reverse clutch, the first forward clutch,and the second forward clutch.

In any of the aspects or combinations of the aspects, operating thefirst, the second, and/or the third clutches to transition between thetwo drive ranges may include synchronously opening one of the first,second, and third clutches while closing another one of the first,second, and third clutches.

In any of the aspects or combinations of the aspects, openings one ofthe first second, and third clutches and closing another one of thefirst, second, and third clutches may be implemented when a ring gear inthe second planetary gear set allows synchronization of the clutchesthat are synchronously opened and closed.

In any of the aspects or combinations of the aspects, hydromechanicalvariable transmission may further comprise instructions stored in thenon-transitory memory that when executed by the processor, while thehydromechanical variable transmission is operating in a first portion ofthe reverse drive range or one of the two forward drive ranges, causethe controller to: operate the hydrostatic assembly to deliver powerfrom the first or the second planetary gear set to the mechanicalassembly; and instructions stored in the non-transitory memory that whenexecuted by the processor, while the hydromechanical variabletransmission is operating in a second portion of the reverse drive rangeor one of the two forward drive ranges, cause the controller to: operatethe hydrostatic assembly and the mechanical assembly to additivelydeliver power to the first or the second planetary gear set.

In any of the aspects or combinations of the aspects, in a portion ofeach of the reverse drive range and the two forward drive ranges powerflow may be circulated from one of the first and the second planetarygear sets to the hydrostatic assembly and from the hydrostatic assemblyto an input of the mechanical assembly.

In any of the aspects or combinations of the aspects, in a portion ofeach of the reverse drive range and the two forward drive ranges powerflow from the hydrostatic assembly and the mechanical assembly may beadditively combined through one of the first and the second planetarygear sets.

In any of the aspects or combinations of the aspects, the mechanical PTOmay be coupled an input interface that receives rotational input from amotive power source (e.g., prime mover).

In any of the aspects or combinations of the aspects, the group of driveranges may include at least one reverse drive range and two forwarddrive ranges.

In another representation, an off-highway vehicle with ahydrostatic-mechanical variable transmission is provided that includessynchronous forward and reverse clutches rotationally coupled inparallel to one another and rotationally coupled in series with amechanical branch and a hydrostatic branch. Further, in thetransmission, the hydrostatic branch and the mechanical branch arerotationally coupled in parallel.

In another representation, a method for transitioning betweenoperational drive ranges in a hydrostatic-mechanical variabletransmission is provided. The method includes synchronously closing aforward clutch while opening a reverse clutch in a mode changetransient. The transmission further includes a hydraulic branch arrangedin parallel rotational attachment to a mechanical branch and both thehydraulic branch and the mechanical branch are rotationally attached toa pair of planetary gear sets that are coaxial positioned in relation toone another.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevant artsthat the disclosed subject matter may be embodied in other specificforms without departing from the spirit of the subject matter. Theembodiments described above are therefore to be considered in allrespects as illustrative, not restrictive.

Note that the example control and estimation routines included hereincan be used with various powertrain and/or vehicle systemconfigurations. The control methods and routines disclosed herein may bestored as executable instructions in non-transitory memory and may becarried out by the control system including the controller incombination with the various sensors, actuators, and other transmissionand/or vehicle hardware. Further, portions of the methods may bephysical actions taken in the real world to change a state of a device.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example examples described herein, but isprovided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the vehicle and/or transmission controlsystem, where the described actions are carried out by executing theinstructions in a system including the various hardware components incombination with the electronic controller. One or more of the methodsteps described herein may be omitted if desired.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific examples are notto be considered in a limiting sense, because numerous variations arepossible. For example, the above technology can be applied topowertrains that include different types of propulsion sources includingdifferent types of electric machines, internal combustion engines,and/or transmissions. The subject matter of the present disclosureincludes all novel and non-obvious combinations and sub-combinations ofthe various systems and configurations, and other features, functions,and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

As used herein, the terms “approximately” and “substantially” areconstrued to mean plus or minus five percent of the range, unlessotherwise specified.

The invention claimed is:
 1. A transmission system, comprising: ahydraulic pump and a hydraulic motor rotationally coupled in parallelwith a first planetary gear set and a second planetary gear set; whereinsun gears of the first and second planetary gear sets are rotationallycoupled to the hydraulic motor; and wherein a carrier of the firstplanetary gear set is rotationally coupled to a first clutch and asecond clutch; and wherein a ring gear of the second planetary gear setis rotationally coupled to a third clutch.
 2. The transmission system ofclaim 1, wherein the second clutch is a reverse clutch.
 3. Thetransmission system of claim 2, wherein the first clutch and the reverseclutch are each directly coupled to the carrier and are adjacent to oneanother.
 4. The transmission system of claim 1, wherein the first,second, and third clutches are friction clutches.
 5. The transmissionsystem of claim 1, further comprising a mechanical power take-off (PTO)rotationally coupled to a mechanical branch that extends between a powersource and the hydraulic pump.
 6. The transmission system of claim 1,further comprising a mechanical power take-off (PTO) coupled to thehydraulic pump.
 7. The transmission system of claim 1, wherein thehydraulic motor is a fixed bent axis motor.
 8. The transmission systemof claim 1, wherein the hydraulic pump is an axial piston pump.
 9. Thetransmission system of claim 1, wherein the first and second planetarygear sets are coaxially arranged.
 10. The transmission system of claim1, wherein the first and second clutches are axially offset from thethird clutch.
 11. The transmission system of claim 1, wherein thetransmission system is included in an off-highway vehicle.
 12. Thetransmission system of claim 1, further comprising an input interfacethat is configured to rotationally couple to a motive power source andan output interface that is configured to rotationally couple to one ormore vehicle axles and wherein the input interface is axially offsetfrom the output interface.
 13. A hydromechanical variable transmission,comprising: a hydraulic pump and a hydraulic motor rotationally coupledin parallel with a first planetary gear set and a second planetary gearset; wherein sun gears of the first and second planetary gear sets arerotationally coupled to the hydraulic motor; wherein a carrier of thefirst planetary gear set is rotationally coupled to a first forwardclutch and a reverse clutch; and wherein a ring gear of the secondplanetary gear set is rotationally coupled to a second forward clutch.14. The hydromechanical variable transmission of claim 13, wherein thehydromechanical variable transmission is an infinitely variabletransmission.
 15. The hydromechanical variable transmission of claim 13,further comprising a mechanical power take-off (PTO) coupled to an inputshaft that receives rotational input from a motive power source.
 16. Thehydromechanical variable transmission of claim 13, wherein the firstforward clutch and the reverse clutch are coaxially arranged to oneanother and axially offset from the second forward clutch and the firstand second planetary gear sets.
 17. The hydromechanical variabletransmission of claim 13, wherein the hydraulic motor is a fixed bentaxis motor and wherein the hydraulic pump is a variable displacementaxial piston pump.
 18. The hydromechanical variable transmission ofclaim 13, wherein the first forward clutch, the reverse clutch, and thesecond forward clutch are coupled in parallel with one another.
 19. Apower split transmission, comprising: a hydraulic pump and a hydraulicmotor rotationally coupled in parallel with a first planetary gear setand a second planetary gear set; wherein sun gears of the first andsecond planetary gear sets are rotationally coupled to the hydraulicmotor; wherein a carrier of the first planetary gear set is rotationallycoupled to a first forward clutch and a reverse clutch; and wherein aring gear of the second planetary gear set is rotationally coupled to asecond forward clutch.
 20. The power split transmission of claim 19,wherein the first forward clutch and the reverse clutch are coupled to afirst central shaft that is radially offset from a second central shaftthat is coupled to the second forward clutch.